BANGKOK – Thai police made their first arrest of a senior leader of anti-government protests for violating the country’s emergency law Monday as government officials promised to apprehend other leaders of the movement, too.

The arrest further heightens tensions in Thailand’s three-month-old political conflict in which protesters seeking to overthrow Prime Minister Yingluck Shinawatra have shut down major intersections across Bangkok. Government officials have been threatening for weeks to arrest protest leaders.

Police arrested Sonthiyarn Cheunruethainaitham, the former managing director of news company Tnews, known for its anti-government views, said Department of Special Investigation’s director-general Tharit Pengdit. He described Sonthiyarn as “a chief-of-staff” for the movement and “second most important figure” after protest leader Suthep Thaugsuban.

“We will continue arresting more protest leaders who have violated the law in the same way,” Tharit said.

Arrest warrants have been issued for 19 leaders of the anti-government protests on the charges of violating the special law and authorities on Monday were seeking the court’s approval for 13 other leaders on the same charges.

The arrest happened just hours after six street cleaners were injured — two seriously — by a small explosion at a protest site in downtown Bangkok. At least 10 people have been killed and scores hospitalized during the political upheaval.

The demonstrators, who mostly draw their support from the urban middle and upper class and those in the south, want Yingluck to step down to make way for an interim appointed government to implement what they say are necessary reforms to fight corruption.

She has refused to resign, arguing she was elected by a large majority and is open to reform, but that such a council would be unconstitutional and undemocratic.

Her government invoked the emergency decree last month following increasing attacks at protest sites prior to the Feb. 2 general election, allowing authorities to ban public gatherings, impose curfews and censor local news reports. The emergency decree, in effect for 60 days, also gives police expanded powers to make arrests, conduct searches and seize suspicious materials.

Sonthiyarn was apprehended at a hotel in northern Bangkok and is being held for questioning at a border patrol police base in the capital’s northern outskirts. Under the state of emergency, a suspect can be held for 30 days without being charged, but police must seek request for detention every seven days.